The proposed research involves an investigation of steroid hormone metabolism in three reproductive organs, the ovary, placenta, and testis. Emphasis is placed on the key role of estrogen biosynthesis in reproductive function, the hormonal regulation of gonadal steroidogenesis, and a comparison of species differences in the process being studied. Human ovarian function will be studied in some detail and will be compared to information obtained in laboratory animal models. The functional cooperation between the antral, granulosa, thecal, and interstitial compartments will be stressed. The mechanism of gonadotropin action on isolated ovarian compartments from the hamster will focus on differential effects on cyclic nucleotide concentration and localization, ornithine decarboxylase activity, and resultant steroid hormone biosynthesis. The biochemistry of androgen aromatization will be studied in the human placental system. Using promising solubilization techniques, the purification of different species of the aromatase and its cytochrome P-450 component will be continued. Testicular estrogen biosynthesis will be studied in immature rats, with special regard to the regulation of aromatase activity and its cellular localization. Parabiotic union of castrate male-intact male rats, in which circulating gonadotropin and estrogen levels are high, will provide a physiological model in which to study testicular aromatization.